The long-term product goal of this project is a small molecule therapeutic to treat rheumatoid arthritis (RA), which acts by reducing the inflammatory response triggered by the pro-inflammatory cytokine macrophage migration inhibitory factor (MIF). Since MIF is an upstream regulator of the inflammatory cascade, small molecule therapeutics targeting MIF activity are expected to provide effective treatment for RA, which currently afflicts 4 million people in the US alone and for which there is no curative therapy. To this end, in Phase I of this SBIR project, we screened 200,000 compounds for MIF inhibitors and identified a number of small molecules that block MIF-driven cellular activation pathways that are associated with the immunopathology of RA. For this proposal we selected two inhibitors that are structurally unique and possess functional groups that have not been previously associated with MIF inhibitory activity. They appear to interact with MIF by distinct mechanisms, and they are not cytotoxic to mammalian cells. In the continuation of this project, we propose to elucidate their precise mechanisms of action by obtaining MIF-inhibitor co-crystal structures. Further, using medicinal chemistry guided by structural data, we propose to obtain structure-activity relationships and modify the compounds to improve their MIF-inhibitory activities in an effort to obtain molecules that are efficacious in the RA mouse model. All of these efforts are expected to yield a lead compound suitable for further development towards a small molecule therapeutic for RA.